Growth, Feed Utilization and Blood Metabolic Responses to Different Amylose-amylopectin Ratio Fed Diets in Tilapia (Oreochromis niloticus)

Abstract

A feeding trial was conducted in tilapia to determine the growth performance, nutrient digestibility, digestive enzymes, and postprandial blood metabolites in response to different dietary amylose-amylopectin ratios. Five isonitrogenous and isolipidic diets containing an equal starch level with different amylose-amylopectin ratios of 0.11 (diet 1), 0.24 (diet 2), 0.47 (diet 3), 0.76 (diet 4) and 0.98 (diet 5) were formulated using high-amylose corn starch (as the amylose source) and waxy rice (as the amylopectin source). Each diet was hand-fed to six tanks of 15 fish each, three times a day over a 6-wk period. After the growth trial, a postprandial blood metabolic test was carried out. Fish fed diet 2 exhibited the highest percent weight gain and feed efficiency and protein efficiency ratio, whereas fish fed with diet 5 showed the lowest growth and feed utilization among treatments. The digestibility for starch in fish fed diet 1 and 2 was higher than those in fish fed with other diets (p<0.05). The highest activities for protease, lipase and amylase were found in fish fed the diet 2, diet 1, and diet 1 respectively among dietary treatments, while the lowest values for these indexes were observed in fish fed the diet 3, diet 5 and diet 4, respectively. The liver glycogen concentrations in fish fed diets 4 and 5 were found higher than in fish fed other diets (p<0.05). The feeding rate, hepatosomatic index, condition factor, and plasma parmeters (glucose, triglyceride, total cholesterol, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol) did not differ across treatments. In terms of postprandial blood responses, peak blood glucose and triglycerides were lower after 3 or 6 h in the fish fed with diets 3-5 than in the fish fed diet 1, but delayed peak blood total amino acid time was observed in fish fed with the diets 1 or 2. The lowest peak values for each of the three blood metabolites were observed in fish fed diet 5. The results indicate that high-dietary amylose-amylopectin ratio could compromise growth, but help in reducing the blood glucose stress on fish caused by postprandial starch load.

Keywords: Amylopectin; Amylose; Performance; Postprandial Response; Tilapia.

Figure 1

Effect of amylose-amylopectin ratios on the plasma glucose concentrations in the fish at different diets. Plasma glucose concentrations were measured at various time intervals after a meal in fish fed diets varying in amylose-amylopectin ratios (0.11, 0.24, 0.47, 0.76 and 0.98, respectively) over the 6-wk feeding period. Data are means±SD (n = 3), represents three replicate tanks used at each sampling time. Plasma samples of three fish were pooled for tank. Plasma glucose was significantly affected by dietary treatments and time after a meal.

Figure 2

Effect of amylose-amylopectin ratios on the plasma triglyceride concentrations in the fish at different diets. Plasma triglyceride concentrations were measured at various time intervals after a meal in fish fed diets varying in amylose-amylopectin ratios (0.11, 0.24, 0.47, 0.76 and 0.98, respectively) over the 6-wk feeding period. Data are means±SD (n = 3), represents three replicate tanks used at each sampling time. Plasma samples of three fish were pooled for tank. Plasma triglyceride was significantly affected by dietary treatments and time after a meal.

Figure 3

Effect of amylose-amylopectin ratios on the plasma total amino acid concentrations in the fish at different diets. Plasma total amino acid concentrations were measured at various time intervals after a meal in fish fed diets varying in amylose-amylopectin ratios (0.11, 0.24, 0.47, 0.76 and 0.98, respectively) over the 6-wk feeding period. Data are means±SD (n = 3), represents three replicate tanks used at each sampling time. Plasma samples of three fish were pooled for tank. Plasma total amino acid was significantly affected by dietary treatments and time after a meal.